The present invention relates to a shaft sleeve made of ceramics, and more particularly to a shaft sleeve made of ceramics which is provided in confrontation with a stationary sliding member in a sliding bearing or a plain bearing and preferably used for a submerged bearing in a pump for handling liquid containing hard solid material.
Conventionally, a shaft sleeve made of ceramics is applicable to various usages because of its excellent wear resistance.
FIGS. 5(a) and 5(b) are a cross-sectional view and a side view, respectively, showing a conventional shaft sleeve. In FIGS. 5(a) and 5(b), a shaft sleeve 1 is of a cylindrical shape having an inside diameter and an outside diameter formed concentrically. A shaft (not shown) is fitted with the inside diameter of the shaft sleeve 1. Groove-like notches 2 are formed in a right end of the shaft sleeve 1.
FIGS. 6(a) and 6(b) are a front view and a cross-sectional view, respectively, showing an engaging member 3 for preventing the shaft sleeve 1 from rotating relative to the shaft. The engaging member 3 is formed, on the inside surface thereof, with a key way 4 with which a key (not shown) attached to the shaft is fitted, so that the engaging member 3 is fixed to the shaft and rotated integrally with the shaft. The engaging member 3 is formed, on the left end thereof, with projections 5 which are fitted with the notches 2 of the shaft sleeve 1, whereby the shaft sleeve 1 of FIGS. 5(a) and 5(b) is prevented from rotating relative to the engaging member 3 and is rotated integrally with the shaft.
FIGS. 7(a), 7(b) and 7(c) are a front view, a side view and an upper plan view, respectively, showing another type of engaging member 13 which is used in conjunction with the shaft sleeve 1 (see FIGS. 5(a) and 5(b)) fitted with a spline shaft. In FIGS. 7(a), 7(b) and 7(c), the engaging member 13 is formed of sheet metal such as a steel plate and has at the inside surface thereof projections 14 which are fitted with a spline groove of the shaft (not shown). Further, the engaging member 13 is provided at the left end with projections 15 which are fitted with the notches 2 of the shaft sleeve 1, thereby preventing the shaft sleeve 1 from rotating relative to the shaft.
As mentioned above, the shaft sleeve 1 is prevented from rotating relative to the shaft and is rotated together with the shaft by the use of the engaging member 3 (see FIGS. 6(a) and 6(b)) or the engaging member 13 (see FIGS. 7(a)-7(c)). That is, in order to prevent the shaft sleeve from rotating relative to the shaft, the engaging member which comprises a different member from the shaft sleeve is required, and the end of the shaft sleeve must be machined to form a groove to engage with the engaging member. However, in the case where the shaft sleeve 1 is made of ceramics, ceramics are brittle and weak in tensile stress, although they are hard. Further, when the shaft sleeve made of ceramics is in operation, stress concentration occurs at the groove-shaped notches 2, and the shaft sleeve can be easily damaged or broken. Further in the case of the spline shaft, as shown in FIG. 8, the shaft sleeve 21 is in contact with the spline shaft 22 at the contacting portions 23 corresponding to the projecting portions of the spline shaft 22. Therefore, the central portions 24 between the adjacent contacting portions 23 are subjected to bending stress. As a result, the shaft sleeve may be damaged or broken.
On the other hand, conventionally, there is a widely used pump which handles liquid having a temperature of 0.degree. to 120.degree. C. In this case, between the shaft sleeve and the shaft, a clearance of about 2/1000 with respect to the outside diameter of the shaft is required due to the difference in thermal expansion coefficients between the shaft sleeve made of ceramics and the shaft made of metal such as stainless steel. For example, if the shaft has an outside diameter of 30 mm, a clearance of 6/100 mm is required. In this case, taking into consideration dimension tolerance besides the above clearance, the clearance of approximately 0.1 mm is required, thus enlarging or enhancing the looseness between the two members at low temperatures.
Further, when the spline shaft or polygonal shaft or the like is employed, the contacting area of the shaft and the shaft sleeve is small, thereby allowing the shaft sleeve to be easily cracked.